This invention relates to improvements in systems for controlling the movement of a train along a railroad track and, more particularly, to a train control system which integrates dynamic and fixed data concerning the route over which the train is traveling and conditions existing on the track ahead, and which provides positive train control based on signal status and an operational profile of the route.
Railroad signalling and train control systems have traditionally been based on the concept of protecting zones of track, called "blocks," by means of some form of signal system that conveys information to the locomotive engineer about the status of one or more blocks in advance of the train. Wayside signal lights located along the track are controlled by electrical logic circuits which use track circuits to detect the presence of a train in any given block, and automatically combine the status of several adjacent blocks to present the proper aspect, or combination of lights, to indicate to the train crew whether the train may proceed at maximum speed, should reduce speed due to more restrictive conditions ahead, or should be brought to a stop. The distance required to slow or stop a moving train is sufficiently long that information must be conveyed to the train at least one full block in advance of where the reduced speed or stop is required.
An alternative approach which is used on portions of some railroad systems is referred to as cab signalling and may be used with or without wayside signal lights. In cab signalling the same logic that determines block status for display on the wayside signals is also used to generate one of several forms of encoded electrical current in the rails, such that block status is represented by the selection of the code rate used. Equipment on the locomotive detects the coded currents through inductive pickup coils located just above the rail and ahead of the lead wheels, and decodes the information to arrive at a status to be displayed in the engine cab in the form of a pattern of lights similar to those used on wayside signals. The particular pattern of lights displayed is called the "aspect" of the signal. Displaying this information in this manner makes the block status visible to the train crew continuously, not just while approaching a wayside signal, and also permits any change in block status to be displayed immediately as it happens rather than at the next wayside signal which may be far ahead and out of sight at the time of the change in status.
Most cab signal systems include some form of automatic train control (ATC) feature which uses one or more methods to assure that the train crew is alert and responding to any changes in cab signal aspects. Some of these systems only require acknowledgement of the change, while others require application of brakes within a minimum time interval as assurance that a more restrictive condition is recognized by the crew.
Cab signal systems, however, employ a code transmitter coupled to the track for the purpose of transmitting the coded currents along the track a desired distance. A problem of sufficient range can occur in long blocks and the presence of the coded current creates a source of possible interference with other track circuits. Therefore, train control systems have been proposed that entirely eliminate wayside signals and the transmission of dynamic data via coded current in the rails, two of which will be discussed briefly below.
U.S. Pat. No. 4,711,418 to John H. Auer, Jr. et al issued Dec. 8, 1987 and is directed to a radio based control system in which the transmission of dynamic data (speed aspect, etc.) is accomplished entirely by radio transmissions from a central control office to the trains traveling along the track. The central office computer is the source of the dynamic data which indicates block status as determined not by track circuits but by location reports transmitted to the central control office from the trains via radio. Fixed data as to distances and location is provided by trackside transponders.
A current ATCS (Advanced Train Control System) industry specification also describes a system which does not involve the wayside signals and, like Auer, determines block status at the central office based on location reports received from the trains and transmits the resulting dynamic data back to the trains in the form of movement authorities. In this proposed system, trackside transponders are used as location reference markers from which actual location is measured by odometer. Additional fixed data, e.g., distance data and civil speed limit data, is stored in master files and maintained at the central office. For an operating train, the portion relevant to the train's route is transferred to on-board memory. Both Auer and the ATCS systems, however, require duplicating, in a central office computer, most or all of the vital logic performed at interlockings and on the rail line between interlockings. This creates the potential for a discrepancy in timing, if not in content, between authorities granted from the central office logic versus those displayed by the wayside signals, some of which must always be maintained as a backup to protect trains in the event of failure of the more sophisticated control system.